1. Field of the Invention
The present invention relates to a key input control system, and more particularly to a hardware status switching control system for switching a hardware status at an arbitrary time, by using a function key.
2. Description of the Related Art
The rapid development of semiconductor technology has produced highly-integrated and high-speed central processing units or CPUs of 16 and 32 bits, for example. Along with the development of these CPU, various personal computers have been developed.
Such a personal computer may be required to switch its hardware status. For example, a CPU clock must be changed. More specifically, when an application to be executed must be processed at high speed such as a single user multitask or a multiuser multitask, the CPU clock must be higher. On the contrary, when a game program for example is executed at the same speed as that of the multitask, an operator cannot play correctly. In this case, the CPU clock must be changed to a low speed in response to an operator's request.
Further, a personal computer which is provided with a flat panel (plasma display or a liquid crystal display) as a standard and which is connectable to a CRT display as an option is required to change the displays depending on an application program to be executed. When the application program uses the CRT display, the computer must change the flat panel display to the CRT display and vice versa.
Further, when a computer is provided with a single font and a double font as a character type to be displayed (printed), the font to be used must be selected.
The hardware status described above may preferably be switched under an operating system program (OS) or an application program being executed.
The above switching has been executed in two conventional methods.
The first method uses a keyboard interrupt. More specifically, in response to a specified function key, a keyboard CPU (a sub CPU) incorporated into a keyboard unit interrupts a main CPU. In response to the interrupt, the main CPU executes a keyboard interrupt routine, determines which key is depressed, and executes a processing corresponding to the depressed key.
However, this method has two drawbacks. First, in most cases, an application program itself performs the keyboard interrupt control. If this is case, the interrupt control included the BIOS (basic input/output system) cannot be executed. Accordingly, a switching control routine included in the BIOS cannot be executed. Second, the switching control is performed by depressing a function key. However, when the function key is assigned to a specific use in the application program, the switching control cannot be performed.
The second method uses a timer interrupt. A main CPU is interrupted at a predetermined period by a time out signal from the timer. In response to the interrupt, the main CPU inquires of a sub CPU incorporated in a keyboard if a predetermined function key is depressed. If the predetermined function key is depressed, a predetermined processing (switching control) assigned to the function key is executed by a basic input and output program (BIOS).
However, the main CPU operates asynchronously with the sub, CPU. Thus, when the main CPU performs the inquire operation, the sub CPU cannot respond to the inquiry promptly and the main CPU, generally, must wait several hundred microseconds for a response. Such delay may cause the main CPU to operate inefficiently or erroneously. For example, assume that the main CPU has been executing a communication program before being interrupted. In a high-speed communication, one character is transmitted at an interval of 100-200 microseconds. Accordingly, the main CPU fails to receive the transmitted character.